Interlock assemblies for replaceable loading unit

ABSTRACT

Interlock assemblies for attaching a loading unit to a surgical stapling instrument are provided. The interlock assemblies are formed on a proximal end of a shell member and on a distal end of an adapter assembly. The interlock assemblies may include a collar member for selectively securing the shell member to the adapter assembly. The collar member may be mounted on the shell member or on the adapter assembly.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a Divisional Application which claims the benefit of and priority to U.S. patent application Ser. No. 14/273,850, filed on May 9, 2014, now U.S. Pat. No. 9,913,643, the entire content of which is incorporated herein by reference.

BACKGROUND

Technical Field

The present disclosure relates to surgical stapling devices including replaceable loading units. More particularly, the present disclosure relates to interlock assemblies for operably securing the replaceable loading units to an actuation assembly of the surgical stapling device and/or surgical adapter assembly.

Background of Related Art

Surgical devices for applying staples, clips, or other fasteners to tissue are well known. Endoscopic stapling devices include an actuation unit, i.e., a handle assembly for actuating the device and a shaft for endoscopic access, and a tool assembly disposed at a distal end of the shaft. Certain of these devices are designed for use with a replaceable loading unit which includes the tool assembly and houses the staples or fasteners. The replaceable loading unit may include staples of various sizes and the staples may be arranged in one or more configurations. After firing the stapling device with a replaceable loading unit, the user may detach the empty replaceable loading unit from the actuation unit, select and attach a second replaceable loading unit to the actuation unit, and fire the stapling device again. This process may be performed repeatedly during a surgical procedure.

Many of the stapling devices include an interlock assembly for selectively attaching the replaceable loading units to the actuation unit. The components of the interlock assemblies are typically located on the elongated bodies of the actuation unit or on adapter assemblies connected to the actuation unit. The sterilization and cleaning of the actuation units and adapter assemblies are complicated because of the location of the interlocking components on the elongated bodies or adapter assemblies.

Therefore, it would be beneficial to have a surgical device in which the components of the interlock assemblies are located on the loading units and, thus do not require sterilization.

SUMMARY

Accordingly, an interlock assembly for attaching a loading unit to a surgical stapling instrument is provided. The interlock assembly includes a shell member, a collar member, and an adapter assembly. The shell member has a proximal end including a first cylindrical portion and a second cylindrical portion and a distal end supporting a staple cartridge defining a plurality of staple retaining slots arranged in a pair of concentric rows. The collar member is received about the first and second cylindrical portion and is moveable between a locked position and an unlocked position. The collar member defines a plurality of slots. The adapter assembly includes a distal end selectively securable to the proximal end of the shell member. The adapter assembly includes a plurality of lugs selectively receivable within the plurality of slots when the collar member is in the unlocked position and secured within the slots when the collar member is in the locked position.

The interlock assembly may further including a torsion spring operably received about the first cylindrical portion for biasing the collar member to the locked position. In one embodiment, the distal end of the adapter assembly is receivable about the first cylindrical portion of the shell member. The first cylindrical portion may include a pair of tabs configured for receipt within a pair of longitudinal slots defined by the distal end of the adapter assembly. The collar member may include an outer surface configured to facilitate operable engagement by a user.

Another interlock assembly for attaching a loading unit to a surgical stapling instrument is provided. The interlock assembly includes a shell member and an adapter assembly. The shell member has a proximal end defining a pair of openings and a distal end supporting a staple cartridge defining a plurality of staple retaining slots arranged in a pair of concentric rows. The adapter assembly includes a distal end securable to the proximal end of the shell member, the adapter assembly including a pair of arms each including a protrusion of a free end thereof, wherein each of the protrusions are received within the pair of openings when the distal end of the adapter assembly is received within the proximal end of the shell member. The distal end of the adapter assembly may define a ledge configured to engage a proximal surface of the proximal end of the shell member when the distal end of the adapter assembly is received within the proximal end of the shell member to facilitate alignment of the pair of protrusions with the pair of openings. The pair of arms may be flexible radially inward.

Still another interlock assembly for attaching a loading unit to a surgical stapling instrument is provided. The interlock assembly includes a shell member having a proximal end that includes a first threaded portion and a distal end that supports a staple cartridge defining a plurality of staple retaining slots arranged in a pair of concentric rows. The interlock assembly further includes an adapter assembly that includes a distal end having a flange receivable within the proximal end of the shell member and a second threaded portion disposed proximal of the flange. The interlock assembly also includes a collar member received about the distal end of the adapter assembly and includes an internally threaded portion in engagement with the second threaded portion. The collar member may be moveable into selective engagement with the first threaded portion when the flange of the adapter assembly is received within the proximal end of the shell member. The collar member may include an outer surface configured to facilitate selective engagement by a user.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the disclosure and, together with a general description of the disclosure given above, and the detailed description of the embodiment(s) given below, serve to explain the principles of the disclosure, wherein:

FIG. 1 is a perspective view of a replaceable loading unit, according to an embodiment of the present disclosure, and a distal end of an adapter assembly, according to an embodiment of the present disclosure;

FIG. 2 is a perspective view of the loading unit shown in FIG. 1 selectively attached to the distal end of the adapter assembly shown in FIG. 1;

FIG. 3 is an exploded perspective view of the replaceable loading unit shown in FIG. 1;

FIG. 4 is a perspective view of the proximal end of the replaceable loading unit shown in FIG. 1 with a collar member removed;

FIG. 5 is a cross-sectional perspective view of a collar member of the replaceable loading unit shown in FIG. 1;

FIG. 6 is a cross-sectional perspective side view of the loading unit shown in FIG. 1 with internal components removed;

FIG. 7 is a side view of the replaceable loading unit shown in FIG. 1 and the distal end of the adapter assembly shown in FIG. 1, prior to attachment of the loading unit to the adapter assembly;

FIG. 8 is a perspective end view of the distal end of the adapter assembly shown in FIG. 1 and a perspective view of the proximal end of the replaceable loading unit shown in FIG. 1;

FIG. 9 is a side view of the interlock assembly of the replaceable loading unit and adapter assembly shown in FIG. 1 prior to receipt of a lug of the adapter assembly within a bayonet-type slot of the loading unit;

FIG. 10 is a side view of the interlock assembly of FIG. 1 upon receipt of the lug of the adapter assembly within the slot of the loading unit;

FIG. 11 is a side view of the interlock assembly of FIGS. 9 and 10 with the lug of the adapter assembly secured within the slot of the replaceable loading unit;

FIG. 12 is a cross-sectional perspective view of the replaceable loading unit and distal end of the adapter assembly shown in FIG. 1 with the replaceable loading unit securely attached to the adapter assembly;

FIG. 13 is a perspective view of a replaceable loading unit, according to another embodiment of the present disclosure, and a distal end of an adapter assembly, according to another embodiment of the present disclosure;

FIG. 14 is a perspective view of the replaceable loading unit shown in FIG. 13 selectively attached to the distal end of the adapter assembly shown in FIG. 13;

FIG. 15 is a perspective view of the distal end of the adapter assembly shown in FIG. 13;

FIG. 16 is a cross-sectional perspective view of the replaceable loading unit shown in FIG. 13, with internal components removed, and a cross-sectional perspective view of the distal end of the adapter assembly shown in FIG. 13;

FIG. 17 is a cross-sectional perspective view of a proximal end of the replaceable loading unit and distal end of the adapter assembly shown in FIG. 16, with the replaceable loading unit partially attached to the adapter assembly;

FIG. 18 is a cross-sectional perspective view of the replaceable loading unit and distal end of the adapter assembly shown in FIG. 16, with the replaceable loading unit attached to the adapter assembly;

FIG. 19 is a perspective view of a replaceable loading unit, according to another embodiment of the present disclosure, and a distal end of an adapter assembly, according to another embodiment of the present disclosure;

FIG. 20 is a perspective view of the replaceable loading unit shown in FIG. 19 attached to the adapter assembly shown in FIG. 19;

FIG. 21 is a perspective view of the replaceable loading unit and distal end of the adapter assembly shown in FIG. 19, with a collar member removed;

FIG. 22 is a perspective view of a collar member of the adapter assembly shown in FIG. 19;

FIG. 23 is a cross-sectional side view of the replaceable loading unit shown in FIG. 19, with internal components removed, and a cross-sectional side view of the distal end of the adapter assembly shown in FIG. 19;

FIG. 24 is a cross-sectional side view of the replaceable loading unit shown in FIG. 23 partially attached to the distal end of adapter assembly shown in FIG. 23; and

FIG. 25 is a cross-sectional side view of the replaceable loading unit shown in FIG. 23 attached to the distal end of adapter assembly shown in FIG. 23.

DETAILED DESCRIPTION

Embodiments of the presently disclosed interlock assemblies will now be described in detail with reference to the drawings in which like reference numerals designate identical or corresponding elements in each of the several views. As is common in the art, the term “proximal” refers to that part or component closer to the user or operator, i.e. surgeon or clinician, while the term “distal” refers to that part or component further away from the user.

With reference to FIGS. 1 and 2, an interlock assembly, according to an embodiment of the present disclosure, is shown generally as interlock assembly 110. Interlock assembly 110 is formed on a proximal end 104 of a loading unit 100 and a distal end 152 of an adapter assembly 150. Interlock assembly 110 is configured to operably secure loading unit 100 to adapter assembly 150. Adapter assembly 150 is configured to operably connect loading unit 100 to a surgical stapling device (not shown). Although interlock assembly 110 will be shown and described with reference to loading unit 100 and adapter assembly 150, it is envisioned that interlock assembly 110 may be modified for use on different loading units and with different adapter assemblies. Alternatively, interlock assembly 110 may be modified to be connected directly to an elongate body (not shown) of an actuation assembly (not shown). Loading unit 100 and adapter assembly 150 will only be described to the extent necessary to fully disclose the aspects of the present disclosure.

For a more detailed description of exemplary loading units and adapter assemblies, please refer to commonly owned U.S. Patent Application Publication No. 2013/0181035, the content of which is incorporated by reference herein in its entirety. Exemplary electromechanical surgical stapling devices for operating adapter assembly and/or loading units are shown and described in U.S. Patent Application Publication No 2012/0253329, the content of which is also incorporated by reference herein in its entirety.

With reference now to FIGS. 3 and 4, loading unit 100 includes a shell member 102. Interlock assembly 110 is located on a proximal end 104 a of shell member 102 and includes a first cylindrical portion 106 and a second cylindrical portion 108, a collar member 120, and a torsion spring 130. First cylindrical portion 106 of interlock assembly 110 is configured to be received within a longitudinal opening 151 (FIG. 8) of adapter assembly 150. A pair of lugs 112 extend radially outward from first cylindrical portion 106 and are configured to be received within slots 153 (FIG. 8) formed on an inner surface 152 a of distal end 152 of adapter assembly 150. Second cylindrical portion 108 of interlock assembly 110 is configured to be received within collar member 120 of interlock assembly 110. Second cylindrical portion 108 of interlock assembly 110 defines a pair of notches 111 (FIG. 12) each configured to receive a tab 126 formed on and extending radially inward from a distal portion 124 of collar member 120. As will be described in further detail below, receipt of tabs 126 within notches 111 of second cylindrical portion 108 limits the amount of rotation between collar member 120 and shell member 102. A ledge 114 is formed between first cylindrical portion 106 and second cylindrical portion 108. Ledge 114 defines a hole or aperture 113 configured to receive a first end 130 a of torsion spring 130 of interlock assembly 110.

A distal end 104 b of shell member 102 supports a staple cartridge 140 (FIG. 2). Staple cartridge 140 may be releasable secured to shell member 102 to permit replacement of staple cartridge 140 after firing. Staple cartridge 140 defines a plurality of staple retaining slots 141 arranged in a pair of concentric rows and is configured to retain a plurality of staples (not shown).

With particular reference now to FIG. 5, collar member 120 forms a cylindrical member configured to be rotatably received about proximal end 104 of shell member 102. Collar member 120 includes a proximal portion 122 and a distal portion 124. Proximal and distal portions 122, 124 are separated by a ledge 123. Distal portion 124 of collar member 120 is dimensioned to be received within an opening 131 of torsion spring 130 and ledge 123 is configured to retain torsion spring 130 within collar member 120. Collar member 120 includes a flap 125 configured to engage a second end 130 b of torsion spring 130. As noted above, distal portion 124 of collar member 120 includes a pair of tabs 126 configured to be received within notches 111 (FIG. 12) of second cylindrical portion 108 of interlock assembly 110 and are configured to limit the rotational movement of collar member 120 relative to shell member 102.

Still referring to FIG. 5, proximal portion 122 of collar member 120 defines a plurality of bayonet-type slots 127 for selectively engaging lugs 154 that extend radially outward from adapter assembly 150. Slots 127 are defined by a slanted or angled portion 127 a of proximal portion 122 of collar member 120 and a recessed portion 127 b of proximal portion 124 a of collar member 120. As will be described in further detail below, slanted portions 127 a of collar member 120 are configured to direct lugs 154 of adapter assembly 150 within slots 127 of collar member 120 and recessed portions 127 b of collar member 120 are configured to selectively maintain lugs 154 (FIG. 8) of adapter assembly 150 within slots 127 of collar member 120. Accordingly, slots 127 in collar member 120 correspond in size and location to lugs 154 formed on adapter assembly 150.

As shown, proximal portion 124 of collar member 120 includes four (4) slots 127, however, collar member 120 may include any number of slots 127. It is envisioned that the number of slots 127 may be more then the number of lugs 154 formed on adapter assembly 150. An outer surface 128 of proximal portion 124 may include ridges 128 a or otherwise be configured to facilitate operable engagement by a user.

Turning now to FIG. 6, collar member 120 is shown rotatably received about proximal end 104 of shell member 102. Tabs 126 of collar member 120 are positioned within notches 111 of second cylindrical portion 108 of interlock assembly 110 to limit the rotation of collar member 120 relative to shell member 102.

Torsion spring 130 is received between ledge 114 formed between first and second cylindrical portions 106, 108 and ledge 123 formed between proximal and distal portions 122, 124 of collar member 120. First end 130 a (FIG. 4) of torsion spring 130 is received within hole 113 formed in ledge 112 of shell member 102 (FIG. 4) and second end 130 b (FIG. 5) of torsion spring 130 engages flap 123 a of collar member 120. As will be described in further detail below, torsion spring 130 maintains an angular position/orientation of collar member 120 relative to shell member 102.

With reference now to FIGS. 7 and 8, adapter assembly 150 is operably connected to an actuation unit (not shown) for actuating replaceable loading unit 100. Slots 153 (FIG. 8) are defined on an internal surface 152 a of a distal end 152 of adapter assembly 150 and lugs 154 are formed on an outer surface 152 b of distal end 152 of adapter assembly 150. As noted above, slots 153 of adapter assembly 150 are configured to receive lugs 112 formed on first cylindrical portion 106 of interlock assembly 110 and lugs 154 of adapter assembly 150 are configured to be received within slots 127 of collar member 120 of interlock assembly 110. Distal end 152 of adapter assembly 150 may further include a shelf 156. As will be described in further detail below, shelf 156 is configured to engage a proximal end 106 a of first cylindrical portion 106 of interlock assembly 110 when loading unit 100 is received about distal end 152 of adapter assembly 150.

The operation of interlock assembly 110 will now be described with reference to FIGS. 7-11. With continued reference to FIGS. 7 and 8, loading unit 100 is aligned and/or oriented relative to adapter assembly 150 such that lugs 154 (FIG. 8) on first cylindrical portion 106 of interlock assembly 110 align with slots 153 (FIG. 8) of adapter assembly 150. Turning to FIG. 9, as loading unit 100 is longitudinally advanced over adapter assembly 150, lugs 154 formed on adapter assembly 150 are received within slots 127 formed in proximal portion 122 of collar member 120. In particular, lugs 154 of adapter assembly 150 engage slanted portions 127 a of proximal portion 122 of collar member 120. Engagement of lugs 154 with slanted portions 127 a results in rotation of collar member 120, as indicated by arrow “A” (FIG. 10), in a clockwise direction relative to adapter assembly 150.

Rotation of collar member 120 in the clockwise direction, as shown, permits further advancement of loading unit 100 relative to adapter assembly 150, as indicated by arrows “B”. As collar member 120 is rotated in the clockwise direction, torsion spring 130 is expanded (radially), recreating a spring bias against collar member 120 in the counter-clockwise direction. As loading unit 100 is fully advanced over adapter assembly 150, lugs 154 of adapter assembly 150 are fully received within slots 127.

Turning to FIG. 11, once lugs 154 of adapter assembly 150 are fully received within slots 127 of collar member 120, lugs 154 of adapter assembly 150 align with recessed portion 127 b of proximal portion 122 of collar member 120. The spring bias of torsion spring 130 (FIG. 12), acting on collar member 120, causes collar member 120 to rotate in a counter-clockwise direction, as indicated by arrow “C” in FIG. 11, returning collar member 120 to a pre-rotated position. Rotation of collar member 120 in the counter-clockwise direction, i.e., return of collar member 120 to the pre-rotated position, positions recessed portion 127 b of proximal portion 122 of collar member 120 about lugs 154 of adapter assembly 150, thereby securing loading unit 100 relative to adapter assembly 150.

With reference to FIG. 12, when loading unit 100 is secured to adapter assembly 150, lugs 154 of adapter assembly 150 are securely received within slots 127 of collar member 120 and the proximal end 106 a of first cylindrical portion 106 of interlock assembly 110 engages shelf 156 of adapter assembly 150.

Loading unit 100 may be disconnected from adapter assembly 150 in the opposite manner of connection. Specifically, collar member 120 of interlock assembly 110 may be rotated in the clockwise direction to remove lugs 154 of adapter assembly 150 from within recessed portions 127 b of collar member 120, and loading unit 100 may be retracted longitudinally relative to adapter assembly 150 to withdraw loading unit 100 from about distal end 152 of adapter assembly 150. Second or subsequent loading units 100 may then be attached to adapter assembly 150 in the manner prescribed above.

With reference now to FIGS. 13-18, an interlock assembly, according to another embodiment of the present disclosure, is shown generally as interlock assembly 210. Interlock assembly 210 is formed on a proximal end 204 of a loading unit 200 and a distal end 252 of an adapter assembly 250. Interlock assembly 210 is configured to operably secure loading unit 200 to adapter assembly 250.

With reference to FIGS. 13-16, loading unit 200 is substantially similar to loading unit 100 described hereinabove, and will only be described to the extent necessary to identify the differences therebetween. Loading unit 200 includes a shell member 202 having a proximal end 204 configured to be received about distal end 252 of adapter assembly 250. Proximal end 204 of shell member 202 defines a pair of openings 203. As will be described in further detail below, openings 203 are configured to receive protrusions 258 formed on free ends 256 b of legs 256 formed on distal end 252 of adapter assembly 250.

With reference still to FIGS. 13-16, adapter assembly 250 includes distal end 252 configured to be received within proximal end 204 of shell member 202 and a shelf 254 configured to engage a proximal surface 204 a of proximal end 204 of shell member 202. Distal end 254 includes legs 256 flexibly attached at a first end 256 a thereof. As noted above, protrusions 258 are formed on free end 256 b of each of leg 256.

The operation of interlock assembly 210 will now be shown and described with reference to FIGS. 17 and 18. Referring initially to FIG. 17, distal end 252 of adapter assembly 250 is aligned with proximal end 204 of shell member 202 of loading unit 200. Advancement of adapter assembly 250 relative to loading unit 200, as indicated by arrows “D” in FIG. 18, causes legs 256 on distal end 252 of adapter assembly 250 to flex radially inward thereby permitting continued advancement of adapter assembly 250 relative to shell member 202 of loading unit 200.

Turning now to FIG. 18, engagement of proximal surface 204 a of proximal end 204 of shell member 202 of loading unit 200 with shelf 254 of adapter assembly 250 aligns protrusions 258 on free ends 256 b of legs 256 of adapter assembly 250 to align with openings 203 formed in proximal end 204 of shell member 202 of loading unit 200. Alignment of protrusions 258 with openings 203 permits free ends 256 b of legs 256 to return to an unflexed condition, as indicated by arrows “E” in FIG. 18, in which protrusions 258 of adapter assembly 250 are received within openings 203 of shell member 202 of loading unit 200. Receipt of protrusions 258 on legs 256 of adapter assembly 250 with openings 203 in shell member 202 of loading unit 200 secures loading unit 200 to adapter assembly 250. It is envisioned that one of proximal end 204 of shell member 202 and distal end 252 of adapter assembly 250 may include one or more longitudinal tabs or slots (not shown) and the other of proximal end 204 of shell member 202 and distal end 252 of adapter assembly 250 may include one or more corresponding slots or tabs (not shown) to facilitate alignment of protrusions 258 on legs 256 of adapter assembly 250 with openings 203 in shell member 202 of loading unit 200.

Loading unit 200 is separated from adapter assembly 250 in the opposite manner of attachment. Specifically, protrusions 258 on legs 256 of adapter assembly 250 are depressed radially inward to cause legs 256 to flex such that protrusions 258 are pushed from within openings 203 in shell member 202 of loading unit 200. Once protrusions 258 of legs 256 no longer reside within openings 203 of shell member 202 of loading unit 200, adapter assembly 250 may be longitudinally retracted relative to loading unit 200 to cause the separation of loading unit 200 from adapter assembly 250. One or more subsequent loading units 200 may be attached to and removed from adapter assembly 250 in the manner described above.

With reference now to FIGS. 19-25, an interlock assembly, according to another embodiment of the present disclosure, is shown generally as interlock assembly 310. Interlock assembly 310 is formed on a proximal end 304 of a loading unit 300, a distal end 352 of an adapter assembly 350, and includes a collar member 360. Interlock assembly 310 is configured to operably secure loading unit 300 to adapter assembly 350.

With reference initially to FIGS. 19-21, loading unit 300 is substantially similar to loading units 100 and 200 described hereinabove, and will only be described to the extent necessary to identify the differences therebetween. Loading unit 300 includes a shell member 302 configured to be received about flange 354 formed on distal end 352 of adapter assembly 350. Proximal end 304 of shell member 302 includes a thread portion 306 configured to be engaged by collar 360 that is operatively mounted on distal end 352 of adapter assembly 350.

With continued reference to FIGS. 19-21, distal end 352 of adapter assembly 350 includes flange 354 and a threaded portion 356. A shelf 358 is formed between flange 354 and threaded portion 356 of distal end 352 and is configured to engage a proximal surface 304 a of proximal end 304 of shell member 302 of loading unit 300. Collar member 360, as shown in FIG. 22, is operatively mounted on distal end 352 of adapter assembly 350 (FIG. 19). Collar member 360 includes a threaded internal surface 362 configured to engage threaded portion 356 of distal end 352 of adapter assembly 350 and threaded portion 306 of proximal end 304 of shell member 302 of loading unit 300 when proximal end 304 of loading unit 300 is received about flange 354 of adapter assembly 350 and proximal surface 304 a of proximal end 304 of shell member 302 abuts shelf 358 formed on distal end 352 of adapter assembly 350. An external portion 364 of collar member 360 may include ridges 364 a or be otherwise configured to facilitate operable engagement by a user.

The operation of interlock assembly 310 will now be shown and described with reference to FIGS. 23-25. Referring initially to FIG. 23, distal end 352 of adapter assembly 350, and more particularly, flange 354, is aligned with proximal end 304 of shell member 302 of loading unit 300. Adapter assembly 350 is advanced relative to loading unit 300, as indicated by arrows “F” in FIGS. 23 and 24, such that flange 354 of adapter assembly 350 is received within proximal end 304 of shell member 302 of loading unit 300 and proximal surface 304 a of shell member 302 abuts shelf 358 formed in distal end 352 of adapter assembly 350 (FIG. 24).

With reference to FIG. 24, once loading unit 300 is fully received about flange 354 of adapter assembly 350, i.e., when proximal surface 304 a of proximal end 304 of shell member 302 of loading unit 300 abuts shelf 358 on distal end 352 of adapter assembly 350, collar 360 is rotated in a first direction relative to loading unit 300 and adapter assembly 350, about a longitudinal axis “X” of loading unit 300 and adapter assembly 350, as indicated by arrows “G” in FIG. 24, to cause threading engagement of internal threaded surface 362 of collar 360 with external threads 356 formed on distal end 352 of adapter assembly 350 and external threads 306 formed on proximal end 304 of shell member 302 of loading unit 300.

Turning to FIG. 25, engagement of internal threads 362 of collar 360 with external threads 356 on distal end 352 of adapter assembly 350 and external threads 306 on proximal end 304 of loading unit 300 secures loading unit 300 to adapter assembly 350. Loading unit 300 may be separated from adapter assembly 350 in the opposite manner of attachment. Specifically, collar 360 is rotated in a second direction relative to loading unit 300 and adapter assembly 350, about longitudinal axis “X” of loading unit 300 and adapter assembly 350, as indicated by arrows “H” in FIG. 25. Once internal threaded surface 362 of collar 360 is disengaged from external threads 306 formed on proximal end 304 of shell member 302 of loading unit 300, loading unit 300 separated from adapter assembly 350. One or more subsequent loading units 300 may be attached to and removed from adapter assembly 350 in the manner described above.

Although the illustrative embodiments of the present disclosure have been described herein with reference to the accompanying drawings, it is to be understood that the disclosure is not limited to those precise embodiments, and that various other changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the disclosure. 

What is claimed is:
 1. An interlock assembly for attaching a loading unit to a surgical stapling instrument, the interlock assembly comprising: a shell member having a proximal end including a first cylindrical portion and a second cylindrical portion and a distal end supporting a staple cartridge defining a plurality of staple retaining slots arranged in a pair of concentric rows; a collar member received about the first and second cylindrical portion and moveable between a locked position and an unlocked position, the collar member defining a plurality of slots; and an adapter assembly including a distal end selectively securable to the proximal end of the shell member, the adapter assembly including a plurality of lugs selectively receivable within the plurality of slots when the collar member is in the unlocked position and secured within the slots when the collar member is in the locked position.
 2. The interlock assembly of claim 1, further including a torsion spring operably received about the first cylindrical portion for biasing the collar member to the locked position.
 3. The interlock assembly of claim 2, wherein the torsion spring includes a first end received within an opening in the shell member and a second end engaging a tab formed on collar member.
 4. The interlock assembly of claim 1, wherein the collar member includes a pair of tabs received corresponding notches formed in the second cylindrical portion of the shell member for limiting movement of the collar member relative to the shell member.
 5. The interlock assembly of claim 1, wherein the distal end of the adapter assembly is receivable about the first cylindrical portion of the shell member.
 6. The interlock assembly of claim 1, wherein the first cylindrical portion includes a pair of tabs configured for receipt within a pair of longitudinal slots defined by the distal end of the adapter assembly.
 7. The interlock assembly of claim 1, wherein the collar member includes an outer surface configured to facilitate operable engagement by a user.
 8. The interlock assembly of claim 7, wherein the outer surface includes a plurality of ridges. 